Ebola Virus Outbreak among Wild Chimpanzees Living in a Rain Forest of Cote d’Ivoire Erin Goode Erin Goode

Introduction  ~25% of a 43 member troop of wild chimpanzees disappeared or were found dead in the Tai National Park, Cote d’Ivoire  In November 1994, primatologists studying the chimp community in the park found 8 dead chimps, and absences of many others  Epidemiologic survey was done to discover the cause of death

con’t  This is the first outbreak of Ebola to be described in the wild  This article discusses the results of investigations leading to the identification of a new subtype of the Ebola virus (EBO-CI) in chimpanzees

Background: Tai Chimps  Tai National Park is the largest and last remnant of the tropical rain forest belt in West Africa (436,000ha) and last remnant of the tropical rain forest belt in West Africa (436,000ha)  Since 1979, wild chimpanzee troop has been studied in the National Park  The home range of these chimpanzees is ~27 square km, and located in the western park of the park.  A similar outbreak of Ebola also occurred in November 1992 among same chimp troop

Location of October-November 1994 Ebola outbreak among chimps

Background: Ebola virus  Ebola (EBO) epidemics occurred in the Democratic Republic of Congo (DRC) and Sudan in 1976  Investigations did not find the virus in insects or mammals  EBO caused one lethal case in DRC in 1977 and an outbreak in Sudan in 1979  A new subtype of EBO (subtype Reston: EBO-R) occurred in a cynomolgus monkeys colony at a quarantine facility in Reston, Va in 1989

con’t  EBO-R was responsible for 3 other outbreaks in monkeys in the USA in 1990 and 1 in Italy in 1992  Investigations traced the source of these EBO-R outbreaks to a primate exporter in the Philippines  The mode of contamination of this facility has not been determined

Materials and Methods: outbreak investigation  A case of Ebola infection- a chimp from the community who was missing or found dead during Oct, Nov, or Dec of 1994  A definite case- a dead chimp with a confirmed presence of EBO virus via laboratory testing  A probable case- a chimp whose dead body was found  A possible case- a chimp who went missing, with a unexplained disappearance

con’t  Cases identified from daily records of investigators  Date of onset- the first day clinical signs were recorded in the signs were recorded in the chimpanzees (2 cases) or day of disappearance (10 cases) chimpanzees (2 cases) or day of disappearance (10 cases)  This is based on the presumption that chimps isolate themselves after they feel sick  Date of death determined from the condition of the body

Materials and Methods: e pidemiologic investigations  Study done with data available from surveys in Park with the troop since 1979 for identifying risk factors for cases  Study from October to December 1994  Presence and physical status of all chimps recorded on a daily basis  Behaviors noted: sexual activity of females, duration of meat consumption (min) in hunting season, and situation of group

con’t  All social interactions with cases recorded, including: grooming, behavior while discovering dead bodies, and behavior with sick animals  Contact chimp- any chimp observed with direct contact with a case-chimp, during period between 2 days prior to the onset of symptoms and death of the case

Materials and Methods: specimen collection  2 necropsies were conducted in field in November 1994  First necropsy done by investigators not aware of proper sampling methods- samples not usable for classic microbiologic testing  Second necropsy- samples of kidney, spleen, lung, liver, lymph nodes, and intestinal tissue collected from a 45 month old female for histologic and bacteriologic studies. Not tested for viruses

con’t  Blood specimens taken from 3 live chimps during 1 st week in Dec for complete blood cell counts and serologic tests  Blood smears prepared from blood to look for malaria or trypanosome parasites

Materials and Methods: laboratory studies  Tissues fixed and embedded in paraffin wax  4  sections stained with hematoxylin, eosin, and saffron  Immunohistochemistry studies done using a pool of monoclonal antibodies known to cross- react with subtypes of EBO  Mouse polyclonal antibodies prepared with EBO-CI and EBO were also used in immunohistochemical tests  Part of each tissue sample used in bacteriologic investigations

con’t  Platelet, leukocyte, RBC, and WBC counts determined  Hemoglobin and hematocrit levels determined  ELISAs done to identify presence of IgG and IgM antibodies for Rift Valley and Crimean- Congo hemorrhagic fever viruses, hantaviruses, chikungunya, yellow fever, and dengue viruses  ELISAs for IgG and IgM antibodies against EBO and EBO-CI viruses also tested

Results: epidemiologic investigation  Beginning of October 1994 chimp community had 43 individuals: 13 infants, 4 young adults, and 26 adults  From October to December- 12 members died or went missing  Of these: 1 definite EBO case, 7 probable cases, 4 possible cases  None of other 4 missing chimps seen since outbreak

Ebola virus attack rate by age and sex

con’t  Of 12 cases, included 2 infants (virus attack rate = 15%) and 10 adults (attack rate = 38%) rate = 15%) and 10 adults (attack rate = 38%)  No significant differences in attack rates between males and females  Attack rates highest among adults  Mothers of both infant cases also died or disappeared  First case of EBO recorded on Oct. 25, 1994 with last on Nov. 27 th  Geographic distribution of dead chimps shows clustered distribution in most commonly used area of the territory

Results: risk factors  Activities involving case-contact were not significant risk factors. Including touching dead chimps or grooming a case patient  Infants had a very high risk factor when their mother was an EBO case  Chimps engaging in sexual activity from Oct to Nov had a relative risk of 2.5  Chimps who consumed meat had a relative risk of 5.2, the risk increase with quantity of meat ingested

Risk factors during Ebola outbreak

Results: observations  Before outbreak, chimp group fed on fruit from 1 fig tree from Oct  Pigeons seen feeding on same tree everyday  Chimps seen hunting twice from Oct to Nov  First hunt occurred 7 days before outbreak- young red colobus monkey killed and eaten  2 main consumers of monkey were among early cases  Last 2 cases fed on adult red colobus 11 days before disappearing

Results: histopathology  Liver lesions contained many small sites of necrosis  Spleen showed extensive areas of necrosis in the red pulp  Single, large, inclusion bodies in cytoplasm of macrophages of red pulp of spleen, some hepatic Kupffer cells, and hepatocytes  In mesenteric lymph node, cortical pulp showed pyknosis and necrosis of centrofollicular areas

con’t  Several macrophages in lymph nodes contained big inclusion bodies- that were compatible with viral inclusions  EBO-specific immunohistochemistry of liver, spleen, lymph nodes, and lung positive liver, spleen, lymph nodes, and lung positive  Large distribution of virus in all organs  M , esp. vascular M , in spleen and liver were the immunopositive cells were the immunopositive cells  Bacterial cultures and serologic tests for Rift Valley, Crimean-Congo fevers, and chikungunya, hantaviruses negative

con’t  3 live chimps had IgG but not IgM antibodies against yellow fever and dengue viruses  3 live chimps sampled had no antibodies against new subtype EBO-CI

Discussion  Immunohistochemistry diagnosed EBO infection in 1 chimp who died in Nov 1994  During this epidemic, the other dead and missing most likely died from same pathogen  Findings indicate a short illness followed by sudden death  3 surviving chimps with high risk factors for EBO, from eating meat, were negative for EBO-CI  Indicates they were never infected- supports idea that case fatality rate is near 100% in infected

con’t  Lesions described similar to lesions observed in experimentally infected monkeys  Contrary to reports of naturally infected humans and experimentally infected monkeys- no hemorrhagic, thrombotic, or vascular lesions present  But pathologic features of EBO-CI could be different from other EBO infections  Results of risk factors are compatible with dissemination patterns in human EBO outbreaks

Discussion con’t  Chimps not at risk for EBO-CI from touching or grooming infected animal  But very close contact is a risk factor, like sexual activities (low risk) or mother-infant contact (high risk)  During this outbreak, infection seemed to have originated from a point source and spread through community  Data shows that highest risk factor for infection was meat consumption between Sept and Oct

Discussion: Colobus connection?  Chimpanzees may be infected from eating their prey- 85% of which is red colobus  1 st colobus hunted could have been cause for early cases, and 2 nd colobus for last 2  But last 2 infected were in contact with the definite case and therefore may be secondary cases  If colobus are EBO source and carriers, epidemics should occur throughout year/hunting season but it does not

Discussion: C olobus con’t  Red colobus are widely distributed in Tai Forest, 1/3 of monkeys in Park  Colobus may be intermediate hosts, being contaminated at the true reservoir in Oct- Nov at end of chimpanzee hunting season  Red colobus are strictly vegetarian spending most of time in canopy and emergent trees  Their niche might be where EBO virus reservoir goes into hiding  Could be contaminated via virus in food, other animals, or contact with small mammal secretions

Discussion: Fig tree of death?  Before beginning of outbreak, chimp community spent large amounts of community spent large amounts of time in a fruiting fig tree (F. goliath) time in a fruiting fig tree (F. goliath)  Observers saw many birds in the tree during day, and argue that rodents, fruit bats, and other species were feeding there at night tree during day, and argue that rodents, fruit bats, and other species were feeding there at night  This fig tree was a focal point for many species and could have allowed transmission of the virus between species

Discussion: the human role  Habitat has been constantly modified by human migration from northern regions of the forest belt  Process has increased dramatically over last 6 years since start of Liberian civil war  Influx of refugees doubled local populations from early 1992 to early 1993, then again in 1994  Causes increased deforestation –crop activities and poaching in the park, leading to a large farmland and broken forest only 2km from chimp home range

Discussion: results of human interference  Emergence of infectious diseases are often linked to ecologic changes  Environmental and climatological disturbances recorded in Tai could have combined to change parts of the EBO reservoir or parts of its behavior  Outbreak occurred at end of rainy season in Tai, which includes larger numbers of small mammals and insects which could explain outbreaks at that time

Discussion: further studies  Studies to investigate the natural EBO virus reservoir  Study would give better understanding of the transmission mechanisms of EBO within and between species  More research on the capacity for EBO to leave the forest and emerge in human populations

Implications:  There is a current EBO outbreak among critical chimpanzee and gorilla populations throughout Central Africa among critical chimpanzee and gorilla populations throughout Central Africa  Primatologists say that nearly 2/3 of a gorilla population wiped out in Lossi Sanctuary in Republic of Congo. From 1,200 gorillas to 450. Leads to renewed fear for already critically endangered species, including mountain gorillas  This massive gorilla and chimp disaster has drawn the attention of the WHO & UN

References  Some slides quoted from: Formenty, Pierre et al. Ebola Virus Outbreak among Wild Chimpanzees Living in a Rain Forest of Cote d’Ivoire. Journal of Infectious Diseases. Volume 179, February Pp S120-S126.  Tsoumou, Christian. Ebola kills 100 in Congo, wipes out gorillas. 12/s_3346.asp 12/s_3346.asphttp:// 12/s_3346.asp